47* Theory of the Nutrition [BOOK in. 



Some years elapsed before Hales' labours added materially 

 to the progress which had been already made in the study of 

 these processes in vegetation. His important services to 

 vegetable physiology close our present period, but before we 

 pass on to them, we must first notice a few less important 

 writers. The pages of Woodward and Beale on transpiration 

 and the absorption of water are not very valuable contributions 

 to the theory of nutrition. The fact stated by Woodward, 

 that a Mentha growing in water took up and discharged by 

 evaporation through the leaves forty-six times as much water 

 as it retained in itself, was perhaps the most important of all 

 that he discovered, but his own conclusions from it were of no 

 value. 



None of Malpighi's doctrines had from the first excited so 

 much attention as the one which makes the air which is 

 necessary for the respiration of the plant circulate in the spiral 

 vessels of the wood, as it does in the tracheae in insects ; while 

 Grew and Ray after him agreed with Malpighi in the main, his 

 countryman Sbaraglia in 1704 ventured even to deny the 

 existence of such vessels, and before long phytotomy was fallen 

 into such a state of decadence that the question, whether there 

 were any vessels, or as they were then called spiral vessels, at 

 all, was repeatedly affirmed and as often denied again, and 

 ultimately it was thought better in the interest of physiological 

 questions to take counsel of experiment rather than of the 

 microscope. Thus in 1715 Nieuwentyt endeavoured with the 

 help of the air-pump to make the air contained in the vessels 

 issue in a visible form under a fluid. Here we again en- 

 counter the philosopher Christian Wolff as a zealous repre- 

 sentative of vegetable physiology in Germany ; in the third 

 part of his work, ' Allerhand niitzliche Versuche,' 1721, among 

 other experiments he mentions some which confirmed the 

 presence of air in plants ; the question was more interesting, 

 in the state in which physics and chemistry then were, than 

 that of the anatomical character of the air-conducting organs. 



